A Deduction on Wizardry
by Awesome11
Summary: Dumbledore needs help watching Harry in his fifth year, so he calls up the one person who he has collected enough I.O.U.'s from over the years to force him to help. Sherlock Holmes. Sherlock drags along John Watson, who is technically a muggle, and they start their mission to attend Hogwarts, Spy and Harry, Ron, and Hermione, and not blow the place up. After Hound of Baskerville.
1. Sorting

The owl is what really surprised John.

He had been out to get some milk, Sherlock wasn't going to get it, he knew that, and had come through the door into his flat. Sherlock was gone, which wasn't that surprising, he could be on a case, taking a walk, heck he could be sulking in his room for whatever reason, stranger things had happened.

John placed the milk into the refrigerator, right next to a bag with a bloody hand in it, not even phased. He walked into the sitting room and was reaching for the newspaper when he heard a small hoot. His head jerked up blue eyes met beady black ones.

The window was open (must have been Sherlock) and the tawny owl just sat on the arm of one of the armchairs, looking at John expectantly. There was a small note tied to it's leg and John reached over to grab it when the door to the flat slammed open.

"I told them it was the Sitter, it was so obvious, but they just had to demand evidence, didn't they?" Sherlock remarked loudly. So he _had_ been on a case, then. Sherlock took one look at the scene and his bored expression transformed into one of shock, and then knowing. He swooped past John and took the letter from the owl, reading through it quickly.

"Oh, come on!" He said exasperatedly. He turned to the owl. "He can't be serious, can he?" The owl just hooted again as a response. "Well I simply can't do it!"

"Can't do what?" John asked, but was ignored, not that it surprised him much.

"Hmm, but it would be interesting to see if it has changed at all, though I doubt it, that place seemes stuck in time." Sherlock muttered to himself, still contemplating the letter. Sherlock tossed the letter to the side and dove towards a drawer, sifting through it. Dust flew everywhere and he finally pulled out a dark and aged box.

"Ah, here we go." He brushed the dust lightly off of it and was about to open said box until yet another hoot came from the owl. "Ah, yes, you can leave now." The owl flew out the window and John just stood watching the box Sherlock had taken out of the drawer.

Gingerly Sherlock pulled out a long stick, and John saw perhaps the most emotions he'd even seen reflect in Sherlock's eyes. There was a clear disdain held towards the stick, but also a slight bit of longing and bitterness before Sherlock seemed to remember himself and shoo away all the emotions. It was Sherlock's goal not to feel.

"Well, John, I can't very well go to Hogwarts on my own. I suppose now will be a good time to apparate into the Headmaster's office, he said he momentarily put down the shields just so I could pop in and talk to him." Sherlock extended his hand to John but John just glared at him slightly.

"Can you please tell me what's going on for once. What's Hogwarts? What do you mean apparate? What's with the stick?!" He exclaimed and a look of mild surprise crossed Sherlock's features.

"John, is your memory leaving you, I thought I explained it too you just last Monday." John's glared at Sherlock.

"Last Monday I was visiting Harry! You really have to stop doing that." Sherlock seemed to think about that for moment.

"Oh, well then I guess I should tell you. I'm a wizard, John."

* * *

One long explanation later John finally chose to accept the fact that Sherlock was either drugged or telling the truth, Sherlock wouldn't go through that much work to trick him. Sherlock explained that he had to meet with the Headmaster of his old school, Hogwarts, and work some things out.

John finally took Sherlock's hand and then nearly choked to death as he felt himself be squeezed half to death. He found himself standing next to Sherlock facing an old man with a long beard, looking at the nonchalantly.

"Ah, Mr. Holmes, I was wondering when you would come."

"No you weren't you sent me an owl knowing precisely when it would reach my house hold and opened up the protections on the school for that doorway of time; of course you knew when I would be coming." There was a chill in Sherlock's tone, and John had to wonder why the dark haired man held so much contempt towards this man.

"Sharp as ever." The old man turned to John. "You brought a guest. I am Professor Dumbledore, and you are…?"

"Dr. Watson." John shook the man's hand, choosing not to trust the man too much since Sherlock obviously didn't.

"You wanted to discuss something with me?" Sherlock inquired, staring at the Professor with a hardened gaze.

"Mr. Holmes, I was wondering if you could take a year away from your life and return to Hogwarts." Sherlock wasn't even surprised.

"Well that much was obvious, but why? Perhaps you need a teaching post filled? But no, you're wise enough not to let me attempt to teach young kids without killing them in the process. Then to watch a student, Harry Potter of course, but how do you intend to have me do that? More importantly, you've been fine watching him for the past four years, why the sudden change?"

To Dumbeldore's credit he was only slightly taken aback by Sherlock's rapid speech, John sent him an apologetic shrug.

"Well, Voldemort, you remember the stories about him, surely, has created a connection to Harry's mind whether he is aware of it or not. I'm hoping that if I avoid the boy he will successfully manage to break the connection with Voldemort. As for how you're going to watch him, that part is simple, you will attend Hogwarts as a pair of Sixth year transfer students from Durmstrang." Sherlock cocked an eyebrow, his eyes scanned over John for a brief moment.

"I don't know if you realized it, but I'm pretty sure neither Watson nor I could pass for a student. Ah, yes, that's right, you can just use magic." He seemed to spit out the last word. "I will have to decline your offer. I left this world for a reason, I refuse to let you drag me back into it."

"Mr. Holmes, I do believe you owe me a favor, something about bailing you out in your first year after a certain explosion in the potions room." Sherlock scoffed.

"A mild experiment, and that is hardly enough to convince me to come back."

"Or is it?" Dumbeldore waved his wand and suddenly in his hands he held a thick file marked I.O.U.

"Wow." John whistled. "He's pretty thorough.

"Fine." Sherlock spat out, taking back out his wand. "But John and I will both attend. We will be back shortly without things and then you may put the spell on us, but if this year is too boring I will not hesitate to spice things up one my own."

"Mr. Holmes, I assumed you would do that regardless."

* * *

Harry sat at the feast. The sorting had just began, as usual the poor first years looked sacred out of their minds. They were carefully sorted into their houses, they all ate their fill of the food, and then Dumbeldore burst into his speech. Hermione elbowed him in the ribs.

"Harry, I asked you a question." She whispered sternly. Harry turned his attention towards his friend.

"What is it?"

"They haven't put the sorting hat away yet." She said like it was the most important thing ever.

"So, maybe they just forgot." Harry shrugged. Hermione seemed like she was about to argue when the new DADA teacher interrupted Dumbeldore. She burst into a huge feast, talking about how she would change the school, and Harry got a bad feeling in his stomach.

"…and Prohibit, what must be, pro-" But they would never know what they must prohibit, for just then the grand doors burst open. In strutted a tall, thin boy about sixteen with dark curls and high cheekbones. He scanned the entire hall with his icy blue eyes that looked as though they were made from glass.

Next to him walked a slightly shorter boy of the same age. His golden-yellow hair shone and his blue eyes scanned the dining hall well, though he was talking to the boy next to him. The two seemed like they were used to getting themselves into these kinds of situations.

"I knew you'd make us late, Sherlock." The shorter one whispered to his friend.

"Yes, but I had to make sure Mrs. Hudson understood that she was not to touch my things. Plus she made us dinner, and her food is to die for."

"That's true…" The other boy mused. Umbridge sat back down on her chair and Dumbeldore stood back up, a twinkle of knowing in his eye.

"Students, I am pleased to make an announcement. We have two new members of our family this year, both previous students from Durmstrang. They will start in the fifth year, and I will expect you all to welcome them with open arms." Murmurs started to ripple across the room. "Now, they will have to be sorted." Professor McGonagall walked back up to the stool and lifted up the sorting hat.

"Holmes, Sherlock." She called, and the dark haired boy with the mildly bored expression walked up and took his seat.

* * *

'Why hello again, it's been a while since I last took a look into that wonderful mind of yours.' The sorting hat said to Sherlock.

'Obviously.' He thought back to it.

'Hm, well this is a surprise. If at all possible you've become even smarter. As before you aren't for Slytherin, no, a Slytherin would get caught doing half the things you do; you are far too clever for them. You are brave, but all your bravery is linked with your brains, Gryffindor is definitely out. Oh, what's this! Last time I couldn't even consider Huffelpuff, but it appears you have changed. You are by far more loyal than before, to the one boy, hm? Well, as with the first time, your smarts and willing to do whatever is possible for knowledge is your biggest trait. You still belong in…'

"Ravenclaw!" The hat shouted out and the blue table burst into applause and Sherlock began to walk towards the familiar table.

"Watson, John." The old Professor called, and Sherlock managed to see his friend give him a nervous glance before the hat slid over his eyes.

* * *

'Well, well, well, what do we have here?' John jumped slightly as the voice entered his head.

'Um, hello.' He thought back to it.

'A Muggle, oh, I see, your Ravenclaw friend has a plan to keep the fact that your not a wizard a secret.' John moved nervously on the stool. 'Antsy to get sorted, are we? Well, let's take a look. Hmm, you would never fit into Slytherin, you're too just to go there. Ravenclaw isn't the right place either, you're smart, but not quite smart enough to be considered one of them. Huffelpuff seems, perfect for you. You are loyal to your friends, to the point that you would kill for them, well then-' The hat seemed to be about to announce that he would be in Huffelpuff before it stopped short.

'What is it?' John asked.

'It appears that I nearly missed something. Huffelpuff _would_ have been perfect for, except for these memories of the battle field. Huffelpuff are supporters, not fighters. No, you are brave, bravery worthy of…'

"Gryffindor!" John got up and walked over to the red and gold table, a slightly nervous feeling in his gut. He wasn't really that sure about these wizards. He had been wishing that he could be in the same house as Sherlock, but he'd have to make due. He straightened his back slightly. He was a soldier for goodness sakes; he shouldn't let these kids intimidate him.

They were released shortly after that and he was about to be led to his common room, he was looking around so he could talk to Sherlock and find out what his plan was when someone bumped into him. He tried to find that person, and smirk made its way to his face when he saw a dark haired Ravenclaw boy a few meters away.

He looked at his hand and saw that Sherlock had left a note. A letter drop, genius aas always. Show off.

Library

11:00

Our Flat

John scowled slightly. What did Sherlock mean, our Flat, how was that going to tell him where to find Sherlock.

* * *

The tired John was scouring the library, squinting against the darkness. What was Sherlock thinking? The numbers of the books here were weird, they were sorted by different subjects (potions, transfiguration, ect.) and then numbered from one going up, sometimes into the thousands. He imagined that Sherlock loved this place.

Finally he walked down a small aisle marked Muggle Studies and found a table in the center there and Sherlock sitting down at it, reading by a lit candle. Goodness, John almost didn't recognize him when he was so small.

"You're ten minutes late." Sherlock said monotonously.

"Well I would have been on time if you had just told me where to find you."

"I did." Sherlock said, finally looking up from his book.

"No, you didn't." John said, handing the scrap of paper to Sherlock.

"See, I said it would be at the library, and then our Flat. Our flat is in the so called 'Muggle World'" Sherlock made quotations with his fingers. "So in Muggle studies, and our Flat is number 221." Sherlock held up his book slightly and John managed to read the number 221 on the binding.

"Okay, so what's you plan?" John asked, and Sherlock lit up slightly at the idea of showing off what genius he had come up with.

"Well, since you're a muggle and you only have a fake wand, I decided that I will perform both spells that you will be required to perform for both of us." Sherlock looked very proud of himself.

"But, Sherlock, I don't think we'll have every class together, we're in different houses."

"John, Gryffindor and Slytherin have a long running feud, so the teacher will do their bests to keep both of those houses apart at all costs. Most Gryffindor's will beat up the weaker Huffelpuffs, so that one will be avoided two. In retrospect Gryffindor's and Ravenclaws merely dislike eachother, but most Gryffindors ignore Ravenclaw's and the Ravenclaws for the most part are uncaring of the Gryffindor, so we will have most classes together. Furthermore I have requested from the Headmaster that we have all spell required classes together, you will have other classes such as Muggle Studies, Divinitation, and Potions without me since those do not require the use of spells."

"Genius." John muttered and Sherlock beamed. John looked at the parchment littered around the desk, notes written all over them in matriculate but messy cursive. "How long have you been down here?"

"Since the feast." Sherlock replied, focusing back on his book.

"Sherlock, did you eat, or even take a nap?!" John exclaimed.

" No."

"Sherlock!" John felt like an angered mother.

"My body is just transportation." John sighed and Sherlock looked over the books that he had collected on his desk and pulled out a well worn one, John caught a glimpse of the spine and saw that it wasn't from this section of the library. "Here, I think you should try to join during tryouts, maybe I can find a way to get you a broom for practicing, you should read over the book first, however, wouldn't want you breaking your neck." Sherlock turned back to his book once again and John knew he was dismissed.

* * *

Walking back to Gryffindor tower John looked at the book. It was called 'The Art of Quidditch'. It looked like it was some sort of wizard sport. John looked at it in curiosity and decided he'd have to see what exactly it was.

* * *

**Tell me what ya think! I'm erally psyched about his, and if I get enough feedback I'll proabably love it even more! I hope you gusy think it's good, it's an idea I got while waiting for season three... don't cry, don't cry.**


	2. Potions

By the time Harry woke up Seamus had already gotten dressed and left the room. He groaned internally, would this ever pass? Neville shrugged at Harry and Ron gave him a supportive glance. It didn't do much to cheer him up. Glancing around the room he noticed that the new boy, what was his name, John? Well, either way he was gone as well, he probably had listened in on the conversation last night and decided to stay away from Harry like the plague, go figure.

With Harry and Hermione in tow he left through the portrait hole and went down the marble staircase. Hermione, of course, brought up last night.

"So last night Dumbledore was talking about how we need to oppose You-Know-Who, and he was talking about how he need to intimidate him as a group…"

"Are you saying you want us to get all buddy buddy with the Slytherins?" Ron exclaimed.

"All I'm saying is that some inter House unity would be good for us." Just then some 4th year Ravenclaws passed by and instantly got wide eyes and clumped together when they saw Harry.

"Yeah, who wouldn't want to become friends with people like them?" Harry said sarcastically as they entered the Great Hall.

"Hey, even the new kid seems to get it!" Hermione replied indignantly. Harry looked at the Gryffindor table. Among the black, red, and gold robes he caught sight of blue. His eyes looked at sure enough there was the new kid, John, and the other kid who had been sorted in Ravenclaw.

As they approached the pair he could see that John was talking with bright eyes to the first one, his plate had piles of food on it and he was gesturing with a book in hand. The other boy, S something, was nodding every now and then, his face was fairly expressionless except for the occasional tug at his lips into a half smile at something John said. His plate was clean, showing no sign of ever having any food on it.

Harry, Ron, and Hermione took the seats facing the pair. John turned to them with a bright smile on his face, his blue eyes were obviously excited, but they also looked a bit tired, had he stayed up last night?

"Hi, you must be Harry Potter. I'm sorry I didn't introduce myself yesterday, I'm John Watson." The boy stuck his hand out and Harry took it. The dark haired boy rolled his icy eyes. "This is my friend, Sherlock." Harry stuck out his hand for the other boy but was instead met with a gaze that seemed to pierce into his very soul.

"You are an only child-"

"Can you not do this right now?" John said in exasperation, and Harry was curious where exactly Sherlock had been going with that.

"John, it's been days since I last deduced someone of interest." Sherlock turned back to Harry. "You're an only child, but you obviously live with another kid around your age, your Aunt and Uncle are taking care of you. You don't like it there, all three of them beat you up and you are malnourished. Mother and Father are dead." He turned to Hermione.

"You are one of his friends. Big teeth, Muggle born, parents are most likely dentists. You own a cat with long hair. Extremely book smart and enjoys reading. You commonly nag your friends to do their homework, but you usually end up doing a good deal of it for them. Oh, interesting, you also have deep romantic feeling for-"

"Sherlock!" What did I tell you about the personal stuff? Now stop it or I won't make any friends." John said in exasperation.

"Nonsense, you wouldn't make any friends either way, now let me do the last one." His gray orbs turned their attention to Ron. "You have many siblings and are lazy with your school work. Extremely supportive of your friends, but you often feel crowded out, by your siblings, by your friends, you have many expectations you can never meet. You also have a deep feeling for-" John shot him a glare. "…someone but are uncertain about confessing your feeling."

"I'm so sorry, Sherlock, why don't you go over to the Ravenclaw table." Sherlock stood up but placed his hands on the table.

"Did I get it wrong?" He asked them all in general. Harry was still in shock and shook his head. Sherlock gave a triumphant smile and walked away.

"I am so sorry about Sherlock."John repeated.

"H-how did he do that?" Ron stuttered.

"Deducing. He looks at you and makes deductions, just don't ask him that when he's around, he'll tell you everything he sees and goodness that takes a long time." John said with a shrug.

"Fantastic!" Hermione squealed, Harry bet she was in love with Sherlock, but what was it he had been saying, about her already liking somebody?

"Harry!" Angelina called out enthusiastically as she walked towards the black haired boy. "How was your summer?"

"Good Angelina, thanks for asking." He replied with a warm smile.

"I've been made the new captain of the Quidditch team." She said, and Harry's smile got wider. He figured she would get that spot, she deserved it.

"That's great. Tryouts are this Friday at 5 for the new Keeper now that Wood is gone, it would be awesome if you could come." Harry nodded in understanding. Angelina left the table to go and scout out the other members of the team. John looked at Harry with excited eyes.

"Do you suppose I could try out?!" He asked. Harry was slightly taken aback at the boys enthusiasm but nodded his head.

"Yeah, I guess, do you know how to play?" Harry asked. John looked slightly sheepish.

"Well, I've been reading up on it, I haven't actually practiced yet." He rubbed the back of his head self consciously and Harry could finally see the book he had in his hand, it was a book on Quidditch.

Harry opened his mouth to make a comment but just then there was a fluttering of wings and owls flooded into the Great Hall. Hermione took a post of the Daily Prophet from one and Harry was about to comment on it when a huge, long, bag landed in the middle of the table. On it was a single tag with the name John written in messy yet deliberate cursive.

John reached for the bag in awe and tore it open. Harry's mind flashed back to when he got his first broom, through a similar way, and he saw John's excitement that mirrored his own as he revealed the shiny new broom.

John's head whipped around and caught the sight of gray eyes winking at his briefly before they disappeared out of the main hall.

Ron had pulled out his schedule and was looking it over, groaning to himself. Harry and John both got out their schedules as well, John looking at his for the first time.

"Look, we've got History of Magic, Double Potions, Divinitation, and Double Defense Against the Dark Arts." Ron groaned some more before continuing. "Binns, Snape, Trelawny, and Umbridge, all in the same day." John looked at his schedule, which matched his own, and realized something.

History of magic was just note taking, Potions was just mixing ingredients, Divinitation was all just predictions. So Sherlock had basically just meant that he'd have one or two classes with him. Hm, he'd have to think about this.

* * *

History of magic was long a drawling, even for John who was hearing all of this for the first time. He couldn't deny that it felt good to be young again, but it really was a pity that he had to waste it all on school, he wanted to try out his new broom, really badly.

Eventually after the longest of time the class ended and he went to Potions. He probably should have had common courtesy, like the stuff he was attempting to teach Sherlock, but he didn't want to risk being late to his next class, plus it would be good practice for familiarizing himself with the place.

It turned out he had been too fast for his own good and was stuck with waiting outside the door. Eventually he got inside and got to see what he had been waiting for. It was dreary and dark, cauldrons sat next to desks, each one able to hold two people each. It ended with Harry and Ron sitting next to each other and him and Hermione sitting next to each other.

He wasn't a genius like Sherlock, but he liked to think he had picked at least a bit up from him, and even if he hadn't it was evident that something had happened between Ron and Hermione in between classes. He had forgotten how much drama there was at this age. Not that Sherlock was much different.

The Professor, Snape, continued to talk about how he expected the best from them, blah, blah, blah. John didn't really care about passing his classes, it was obvious that Sherlock had no plan to stay for more than a year, but despite himself John was intrigued as the Professor continued to talk about the potion they would be making.

He knew that once he left this school and went back to his world he couldn't use this stuff; there was no way he could get his hands on it. But the Doctor/Military side of him told the Civilian side to shut up, it was important to know these things. Plus Heaven knows a Draught of Peace was what he needed most days with Sherlock.

It turned out that they were working separately today and John wouldn't have to work with Hermione, though he wouldn't have minded, it was nice to work alone. He grabbed everything he'd need quickly and carefully, trying to be his best, but still be efficient.

He had learned a lot about this kind of thing, back in his army days. He had to know any plants that could be good, even be willing to use his own clothes for bandages. If someone got hurt, he had to be sure to treat them as fast as he could, but he had to be careful at the same time, he had lost too many people forgetting that one little fact.

Stirring, adding ingredients, stirring, balancing the heat, and waiting, he looked at his watch as he kept track of the time, occasionally he saw some of the students look at his watch weirdly, maybe they didn't have watches in the wizard world? Oh well, too late to make people un-see it, he couldn't magically wipe their minds, heck, for all he knew the wand Dumbledore had given him was really just a carved stick.

He sighed in relief as a silver vapor finally started to gently rise off of the potion, even just smelling it seemed to calm his nerves. Making the potion had been almost therapeutic, it reminded him slightly of the war, not the deaths or the gun shots, it reminded him of his mates in the barracks, fooling around with them. It reminded him of when they would be called for kitchen duty, and attempting to make something edible from all the rotting vegetable and meat and the stale bread.

Snape came by and looked at his cauldron without commenting on it. John took that as a 'good job, it's fantastic' and put a sample in the flask to be graded.

* * *

John had surprised Hermione, she hadn't known he'd have it in him, to make such a complicated person, but when he started, he seemed to be someone else, his eyes showed a significant aging to them, and memories that she couldn't see flashed before them as he made the Draught of Peace.

Then there was his watch, so he was Muggle born? Why should that surprise her? She wasn't quite sure, but she put the information away for later, it could be useful. Next he was heading to Transfiguration, right? She'd have to ask Ron and Harry about what happened in there.

* * *

**Thank you for all the reviews, they were a pleasant surprise. I didn't expect so much support. So, here's chapter two, hope it's all that you wanted ;)**


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